As disclosed in the following patent documents 1 and 2, for example, conventional control systems for a brushless motor is configured to position a rotor to a predetermined angular position before driving a brushless motor thereby to ensure starting of the brushless motor. According to the conventional system disclosed in patent document 1, a rotor is positioned by supplying a DC current from a specified one phase coil (W-phase) to the other phase coils (U-phase and V-phase) of a stator coil set forming a motor by an inverter circuit. According to the conventional system disclosed in patent document 2, a rotor is positioned by supplying a current from a specified one phase to the other phase of a stator coil set two times while changing phases of the stator coil set. Thus, even when a rotation angular position of a rotor is near an electrical angle at an angle 180° (dead point), at which the rotor is uncontrollable relative to a final angle to be positioned, the rotor is made to be controllable to the final angle.
[Patent document 1] JP-A-2009-268169
[Patent document 2] JP-A-2009-165297 (US 2009/0174350 A1)
It is assumed here as one example that a brushless motor control system has a main ECU and a motor controller separately. The main ECU is provided to determine an output a target value (for example, a target rotation speed) related to control for a brushless motor. The motor controller is provided to control current supply to the brushless motor actually.
When electric power is supplied to this control system to start its motor control operation, the main ECU calculates a target value for controlling the brushless motor based on signals of various sensors and switches and transmits a calculated target value to the motor controller. The motor controller recognizes, upon receiving the target value, that the brushless motor need be started to operate. The motor controller positions the rotor first and then controls a rotation state of the brushless motor in accordance with a received target value.
According to the control system described above, after the power supply is started and before the brushless motor is started to operate, it is required to perform many processing, which includes target value calculation by the main ECU, target value transmission from the main ECU to the motor controller, rotor positioning by the motor controller and the like. Thus the control system needs long time before the brushless motor is actually started and brushless motor starting performance is low.